Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed.
The aforementioned process initiates with evaluation of the subterranean formation from which the natural resource is to be recovered. The evaluation may begin with retrieval of samples of the formation and reservoir for laboratory analysis. In particular, for a wellbore, the method may initiate with the gathering of information to produce a well log. Well logging is a technique for providing information to a formation evaluation professional or driller regarding the particular earth formation being drilled. Such information typically includes the characteristics of the earth formations traversed by the wellbore, and the location of subsurface reservoirs of the natural resource. A common method employed in well logging involves imaging of the wellbore using techniques such as acoustic imaging, azimuthal density neutron imaging, and resistivity imaging. Of the three, resistivity imaging is particularly advantageous in terms of the relative simplicity of operation, rapid acquisition of real-time data, and highly accurate images of geological features.
Resistivity imaging techniques are based on measurements of the electrical resistance of the formation exposed to the wellbore. Tools based on this technique typically apply an alternating current of approximately one volt at an operating frequency of about 15 kHz. The current is applied to the formation through a series of pads that are pressed firmly against the wellbore. After passing into the formation, the signal is conducted back to a detector on the tool by a wellbore fluid. The electrical conductivity of the wellbore fluid directly affects the quality of the resolved image. If the wellbore fluid is overly conductive a poorer image may result due to an electrical short preventing good electrical penetration into the formation. If the fluid behaves as a dielectric or a capacitor, the lack of a signal or an unfavorable signal-to-noise ratio may prevent satisfactory image resolution. Such dielectric behavior is often exhibited by wellbore servicing fluids comprising traditional oil-based muds (OBM). The continuous hydrocarbon phase of an OBM is an electrical insulator, causing the mud to behave in a dielectric manner and limiting the utility of these wellbore fluids in resistivity imaging. For example, resistivity measurements in oil based drilling fluids often employ special tools which are not easily accessible to all operators or regions. Therefore, there is continuing need and interest in developing oil-based wellbore servicing fluids with improved conductivity and with expanded ability to be used in resistivity imaging applications.